Recent precipitation trends in Peninsular Spain and implications for water infrastructure design

Study region: Peninsular Spain.Study focus: There is strong evidence that climate change has produced a decrease in precipitation combined with an increased frequency, intensity and magnitude of high-intensity storm events in Peninsular Spain. Such events have been particularly recurrent on the Spanish Mediterranean coast in recent years. This study's first objective is to update the trends in the magnitude and seasonality of precipitation in Spain from 1951 to 2019 at different time scales. Secondly, we analyse how extreme precipitation events recorded in recent years can modify water infrastruc-ture design flows. A QGIS plugin was programmed using Python to calculate the design flows in accordance with the methodologies legally established in Spain.New hydrological insights for the region: The results confirm the decreasing trend in annual pre-cipitation in most of the Spanish territory. This decrease was particularly significant during March and June. Moreover, the average increases of around 30-40 % in design flows, which reached double the values obtained in the reference period of 1951-1990 in some basins, confirm the relevance of incorporating high-intensity storm events recorded in recent years into flow calcu-lations in Peninsular Spain. Design flows obtained without using the most recent rainfall data can be underestimated, with profound risk implications. Therefore, there is a sufficient technical basis to draw attention to this problem and recommend its formal consideration by competent authorities.

Automated summary

This study updates the trends in precipitation in Peninsular Spain and finds a decreasing trend in annual precipitation, especially in March and June. The study also shows that high-intensity storm events have increased in frequency and intensity, resulting in a significant increase in design flows in some basins. It suggests the importance of considering recent rainfall data in flow calculations to avoid underestimating the risk.